Myria:I need to look up why climbing Mt. Everest is only feasible in May.

Weather. The monsoons hit in the summer and just make the weather such that climbing Everest is anywhere from ill advised to potentially suicidal, though people have climbed it during the summer months. Another issue is that due to summer warming the Khumbu icefall is less solid than usual and given several routes cross it, that's a concern. Even under ideal conditions a person can have a part of the icefall just give way under them and fall into a crevasse or have a big ass chunk of ice fall on them. Indeed you're just as likely, if not more likely, to die crossing the icefall than from exposure up at high altitude on Everest.